Hearing loss, which may be due to many different causes, is generally of two types: conductive and sensorineural. Of these, conductive hearing loss occurs where the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the auditory ossicles. Conductive hearing loss may often be helped by use of conventional hearing aids, which amplify sound so that acoustic information reaches the cochlea and the hair cells. Some types of conductive hearing loss are also amenable to alleviation by surgical procedures.
Sensorineural hearing loss, on the other hand, is due to the absence or the destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. Thus, people who suffer from sensorineural hearing loss are unable to derive any benefit from conventional hearing aid systems.
To overcome sensorineural deafness, numerous cochlear implant systems—or cochlear prosthesis—have been developed which seek to bypass the hair cells in the cochlea by presenting electrical stimulation to the auditory nerve fibers directly, leading to the perception of sound in the brain and at least partial restoration of hearing function. To facilitate direct stimulation of the auditory nerve fibers, an array of electrodes which are responsive to a suitable external source of electrical stimuli and which transmit those stimuli to the auditory nerve fibers may be implanted in the cochlea.